Structural effects in solvolytic reactions. VII. Solvolysis of optically active threo-4-phenyl-3-hexyl tosylate. Need for a revision of previous results

Abstract

The acetolysis and formolysis of optica1ly active threo-phenyl-3-hexyl tosylate have been reexamined. It was previously reported that the solvolysis of this compound proceeds with high stereospecificity (predominant retention), similar to that observed in the threo-3-phenyl-2-butyl system. However, in contrast to the largely racemic nature of the retained product from the 3-phenyl-2-butyl derivative, the retained product obtained in the acetolysis or formolysls of the active hexyl derivative was reported to contain 6-8% of the optically active isomer. As the polarimetric to titrimetric rate ratio is 3.3 in the acetolysjs of this compound, a major amount of active retained product (ca. 21 %) is indicated in the absence of racemization arising from internal return. As a part of our investigation in the nature of the reaction pathways involved in solvolysis of secondary β-arylalkyl derivatives, we undertook to reexamine this system in detail with a hope of clarifying the nature of the pathway leading to this active retained product, This study revealed that the acetolysis gives retained product with only approximately 1% of the active form and that the formolysis proceeds to yield completely racemic threo-formate. Consequently, these results remove the reported discrepancy between tbe solvolytic behavior of the 3-phenyl-2-butyl and the 4-phenyl-3-hexyl systems.